This invention relates generally to blow molding machines and more particularly to a blow molding apparatus for producing a container with a translucent view stripe on the mold part line on the container.
Plastic containers, such as motor oil containers, are generally made of an opaque colored plastic resin to provide product identification for consumers. A disadvantage of opaque containers is that it is not possible to visually monitor the level of the container contents. One solution for ascertaining the level of contents in an opaque plastic container is to form the container with a vertical stripe of a translucent plastic resin in the side wall of the container. In this invention the opaque containers are provided with translucent plastic view stripes on the mold part lines on the containers. The location of the view stripe on the container part lines enables the manufacture of containers with view stripes confined to the side wall. This avoids the unusual look of having stripes running through the top and bottom of the container where, in many cases, such stripes are useless.
An accumulator head for a blow molding machine for producing storage drums having a view stripe is disclosed in copending patent application Ser. No. 170,784 filed Mar. 21, 1988 now U.S. Pat. No. 4,802,833, issued Feb. 7, 1989, and commonly assigned.
It is an object of this invention to provide an improved blow molded container with a view stripe on the part line and apparatus for making such a container on existing blow molding machinery, such as reciprocating screw type blow molding machines.
It is a further object of the invention to provide a machine in which the view stripe can be accurately positioned in the parison of opaque plastic from which the container is formed.
The apparatus of this invention utilizes a multi-cavity die head assembly for producing multiple parisons each having a translucent view stripe through the wall of the parison. A manifold assembly is used to supply a primary and a secondary resin to each of the die heads. A primary reciprocating screw extruder is used for extruding a primary resin which is pigmented and opaque. A secondary reciprocating screw extruder is used for extruding a secondary resin of the same or similar type as the primary resin only unpigmented such that it is translucent.
The primary and secondary resins are fed into the interior cavity of each die head at locations diametrically opposite each other. The mandrel sleeve is equipped with a diverter sleeve which divides the flow of the primary resin into two flow streams flowing in opposite directions around the mandrel sleeve. The diverter also directs the flow from a horizontal direction to a vertically downward direction. As the primary resin flows downward and around the mandrel sleeve, a vertical gap is formed between the two flows of primary resin at the opposite side of the mandrel sleeve from where the primary resin is fed into the die head.
A secondary unpigmented resin is inserted into the die head and directed downward into the gap between the primary resin forming a weld of the primary resin. As a result, a tubular parison is created having a vertical stripe of a translucent resin in the wall of the parison.
This tubular parison is then ejected through an annular outlet at the bottom of the die head. The blow mold is positioned below the die head outlet such that the mold halves can then be closed upon the parison. The mold halves are oriented relative to the parison such that the parting line between the mold halves is aligned with the view stripe of the parison. When blow air is injected into the mold to mold the parison to the desired shape, the view stripe is blown into engagement with the parting line, thereby forming a container in which the view stripe is on the parting line.
The advantage of placing the view stripe on the parting line of the mold halves is that the view stripe length can be limited to the side wall of the container. If not located at the parting line, the view stripe will continue across the top and bottom walls of the container to the center of the top and bottom walls.
In producing a bottle in which the fill opening is off center, the mold is shifted to one side after closing upon the parison. The blow pin is then extended into the fill opening of the bottle and the blow air injected into the bottle forcing the parison against the inner wall of the mold cavity to produce a bottle having a shape of the mold cavity.
A container is thus formed which includes a vertical view stripe of a translucent resin through the side wall of the container along the parting line of the two mold halves. By locating the view stripe on the mold parting line, the view stripe of the side wall can, in some cases, end up as flash extending above the side wall which is removed so that the view stripe conveniently ends at the upper end of the side wall. The molds can be oriented to produce the view stripe on either parting line of the container.
It is within the purview of this invention to use any suitable blow moldable plastic resin that can be utilized in both opaque and natural or translucent forms. In any blow molded container produced by this invention, the two plastic resins must be compatible to join together at the parison weld line. In one form, high density polyethylene for both the opaque and translucent resins provides a container with an excellent view stripe through which the container contents can be readily ascertained.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.